Method of drawing metal blanks



June 1941- 'r. F. STACY METHOD 0F DRAWING METAL BLANKS Original Filed Nov. 5-, 1935 3 Sheets-Sheet 1 Inventor mamas 572, M MM%W attorney June 3, 1941. STACY 2,243,986

METHOD OF DRAWING METAL BLANKS June 3, 1941. F, STACY 2,243,986

METHOD OF DRAWING METAL BLANKS Original Filed Nov. 5, 1955 3 Sheets-Sheet 3 ZZZ VAR/ABLE DEL/VERY PUMPS.

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Enventor T/wmas F522 MQ-M Gttorneg Patented June 3, 1941 ivm'rnon or mmwnzsrar. m.

Thomas F. Stacy, Piqua, @hio, assignor to The French Oil Mill Machinery 00., Piqua, Ohio Original application November 5, 1935, Serial No. 48,382, now Patent No. 2,192,778, dated March 5, 1940. Divided and this application .lune 26, 1936, Serial No. 87,513

6 Claims.

This invention relates to metal drawing presses in which a blank sheet of metal is drawn and deformed into a desired form or configuration. In the drawing of sheet metal from blanks, when deep draws are made, a certain point is sometimes reached at which the metal will tear or rupture. If the speed of drawing is too great, there is further danger of tearing of the metal blank.

This application is a division of my copending application S. N. 48,382 filed Nov. 5, 1935, now Patent No. 2,192,778, for Drawing presses.

An object of the invention is to provide an improved method of drawing metal from blanks, with which exceptionally deep draws will be possible; and with which losses from tearing and rupturing of the metal blanks will be reduced.

Another object of the invention is to provide an improved metal drawing method, with which deeper draws may be made with a minimum of loss from tearing and rupturing of the blanks in the drawing operation; with which the speed of the draw need not be objectionably lessened; and which will be relatively simple, dependable, and easily controlled.

Various other objects and advantages will appear from the following description of an embodiment of the invention, and the novel features will be particularly pointed out hereinafter in connection with the appended claims.

In the accompanying drawings:

Fig. 1 is a diagram of a drawing apparatus and control system constructed in accordance with this invention;

Fig. 2 is an elevation of part of the control mechanism for one of the parts;

Fig. 3 is a transverse sectional elevation through a pilot operated check valve, two of which are employed in the system shown in Fig. 1;

Fig. 4 is a sectional elevation through a control valve which may be used in the system of Fig. 1 for controlling the rate of travel of the main ram;

Fig. 5 is a sectional elevation through another control valve which may be used for maintaining a sustained pressure on the blank holding ring in the system of Fig. 1;

Figs. 6 and 7 are sectional elevations of a control valve used in the system of Fig. 1 for controlling the activity of the auxiliary blank holding rams;

Figs. 8 and 9 are similar elevations of valve mechanism used in the system of Fig. 1 for controlling the activity of the main/ram, and

(Cl. ne -511) Fig. 10 is a diagram similar to Fig. l. but illustrating some modifications in the system.

While many features of the invention may be applied to presses of various types, including mechanical, crank and hydraulic presses, or combinations of them, the improved system is shown, by Way of example, as utilized in connection with a hydraulic press having upon its base a relatively fixed die element ill with a suitable die cavity or recess ii in its upper face. Supported above the base, as usual in hydraulic presses, is a platen l2 which is guided in the usual manner for reciprocation toward and from the base which mounts the die element it. This platen it is operated in both directions by a piston iii projecting into a main cylinder M and forming therewith a double acting main ram, by which the platen I2 is reciprocated in opposite directions. The platen l2 removably mounts a die element It which cooperates with the die cavity H to draw and deform a metal blank l6 into a desired configuration or shape.

The blank I6 is placed on the die element ill across the cavity it, and while it is confined in that position, the cooperating die element l5, during the downward travel of the platen it, will draw and deform the blank until it conforms to the shape of the cavity ll. During the drawing operation it is desirable that the periphery of the blank be held under a sustained pressure in order to prevent wrinkling of the blank while being drawn. For this purpose a blank holding ring or member i1 is disposed beneath the platen l2 and is provided with an aperture or opening I8 through which the die element l5 projects. The ring or member I! is supported by a plurality of pistons l9, which extend upwardly therefrom through apertures 20 in the platen f2, and into auxiliary cylinders 2| so as to form with the cylinders 2i, double acting rams that support and reciprocate the blank holding ring or member l1.

When the pistons I 9 are lowered or forced downwardly, the member or ring I! will engage with the blank I6 and confine-it against the die element ID with a sustained pressure. The details of such drawing presses are well known in the art, and in themselves form no part of the invention, and while the blank holding means may be employed equally well with a mechanical or any other type of drawing press, the means for controlling the pressure of the blank holding ring on the blank is particularly adaptable for use in connection with a hydraulic press in which the drawing platen is reciprocated by hydraulic rather than mechanical means.

The activity of. the auxiliary ram pistons i3 is controlled by a valve 22 illustrated in Figs. 1, 6 and 7, and the activity of the main ram piston I3 is c ntrolled by a valve 23 which is similar in construction to the valve 22. The valve 22 is provided with a valve chamber 24 in which a spool-shaped valve element 25 reciprocates, and reciprocation of the element 25 is obtained by a valve stem 26 extending fromthe element 25 downwardly through the bottom end of the easing of valve 22, and downwardly through a pas sage 27 provided in a lateral extension of the blank holding ring or member H. The lower end of the stem 25 is pivotally connected to one end of a control lever 28, which is pivoted at 29 on a suitable part of the press frame. Intermediate of its ends and above the ring I], the stem 26 carries a collar 30 which is shiftable along the stem 26 into different, desired, adjusted positions in any of which positions it may be secured in any suitable manner such as by a set a screw.

In the particular illustrated example, the stem 26 also extends loosely through an aperture 3| in the platen |2. The neutral or intermediate position of the valve element is shown in Fig. 1, and the other operative positions are shown in Figs. 6 and 7, the element 25 being shiftable into the different positions by the control lever 28 and the collar 30. The liquid for the actuation of the auxiliary rams that control the blank holding ring |'I may be obtained from any suitable source such as a tank 32 of any desired size, and preferably, although not essentially, the liquid in tank 32 is maintained under a pressure suchas under a pneumatic pressure, or by.the use of an accumulator, not shown. Various means for maintaining the liquid in the tank 32 under such pressure are well known and are omitted in the interest of clarity.

A unidirectional, continuously operating pump 33 is connected at its intake side by a pipe 34 to one portion of the tank 32, and at its outlet side is connected by a pipe .35 to a port 36 in the valve chamber 24 approximately midway between its ends and between the flanges 31 and 38 of the spool-shaped valve element 25. One end of the chamber 24 is connected by pipes 39 and 40 to another part of the tank 32, and the opposite end of the chamber 24 is similarly connected by pipes 4| and 42 to the pipe 40 which leads to the tank 32.

When the valve element 25 is in a neutral or intermediate position, such as shown in Fig. 1, the flange 3'! of one end of the spool, bridges and closes an annular port 43 in the side wall of the chamber 24, and this port 43 is connected by a branched pipe 44 to the lower or pull back ends of the auxiliary cylinders 2|, that is to the ends of the cylinders 2| which are beneath the head of the piston l9. Any number of the cylinders 2| may be employed, but only two are shown for the sake of simplicity.

The opposite ends of the cylinders 2|, that is, the upper ends which extend across the entire end areas of the heads of the pistons l9, are connected by a pipe 45 with a port 46 which is aligned with the other flange 38 of the spool of the valve element 25, when the latter is in this intermediate or neutral position shown in Fig. 1. The flange 38, however, instead of brid ing and closing the port 46, when aligned therewith, in the manner that the flange 31 closes the port 43, is bevelled or chamfered off on opposite sides of its peripheral edge so that when this flange 3'7 is aligned with this port 46, as

port 46, and at the same time the flange 31 has uncovered the port 43 so that communication is established between pipe 4| leading to the lower end of the chamber 24 and the port 43., When the valve element 25 is in this upper position shown in Fig. 6, any liquid trapped in the auxiliary cylinders 2| below the heads of the piston, may escape through the pipe 44, port 43, the lower end of chamber 24 and pipes 4| and 42, back to the tank 32. At the same time the pump 33 is withdrawing liquid from the tank 32 through the pipe 34 and delivering it through the pipe 35, port 35, central portion of the valve chamber 24, port 46 and the pipe to .the upper ends of the auxiliary cylinders 2|.

The pistons l9 are now free to descend and the liquid delivered from the pump into the upper ends of the cylinders 2| will urge the pistons l9 downwardly. Until resistance is encountered, however, by the ring l1, its weight will tend to pull the pistons l9 downwardly, and in order to expedite this movement, a preflll check valve 41 is connected at one side through a pipe 48 to the pipe 45, and at its other side by a pipe 49 to the pipe 40. One type 01' such a check valve is shown in Fig. 3. The free check valve element 50 provided in this valve 41, opens freely to pass fluid from the pipe 49 to the pipe 48 and automatically closes to prevent reverse flow. Thus as the pistons I! start downwardly to place the blank holding ring H on the blank IS, the operating liquid will fiow from the tank 32 through pipes 40 and 49 to the valve 41, will open the check valve 50 and pass through the pipes 43 and 45 to the free ends of the cylinders 2| to fill the space created by descending pistons |9. When the auxiliary pistons l9 are to be raised, it is desirable to open the valve 41 and allow the liquid displaced from the upper ends of the cylinders 2| by the pistons l9 to return easily and rapidly to the tank 32. For this purpose a pilot cylinder 41a (Fig. 3), operates a piston 41b against the action of a helical compression spring 410 to lift the valve element 50 forcibly. A branch of the pipe 44 is connected to the pilot cylinder 41a. Hence, whenever operating liquid is supplied to the lower ends of the cylinders 2| to lift the pistons IS, the same operating liquid pressure is applied to the pilot device to lift valve element 50 and allow free return of liquid from the upper ends of cylinders 2| to tank 32, without passage of all of the displaced liquid through the valve 22.

When the blank holding ring I! engages with the blank l5, resistance is immediately ofi'ered to further downward travel of the pistons l9, whereupon, the pressure in the upper ends of the cylinders 2| immediately builds up because of the continued delivery thereto of the operating liquid from the pump 33, and this increased pressure tends to cause a reverse flow through the valve 41. The valve 41 thereupon automatically closes through the seating of its valve element 50, and thereafter continued delivery of the operatingliquid from the pump 33 to the upper ends of the cylinders 2| will cause the building up of a high pressure on the pistons 19 acting in -a downward direction, which pressure is transmitted to the blank holding ring I1 and thus to the periphery of the blank I 6.

It is desirable to maintain a sustained pressure on the ring H in this holding position, and this is accomplished in accordancew-ith this invention by means in addition to the pump 33. For this purpose the port 46 is also connected by a pipe through a valve seat to the valve chamber 52 of a pressure relief valve 53. This pressure relief valve, shown particularly in Fig. 5, has a free valve element 54 which is urged into closed position against its seat by a spring 55 which is compressed between the valve element '54 and a pressure head 56 also disposed in the chamber 52. The pressure head 56 is mounted on a stem 51 which has threaded engagement with the casing of valve 53, so that when this stem or rod 51 is turned or rotated, it will be shifted endwise in the chamber 52 in a direction depending upon the direction of rotation of the stem. The pressure of the spring 55 on the valve element 54 will thus be varied by rotation of .the stem or rod 51. 1

An outlet 58 of the chamber 52 is connected by a pipe 59 to the pipe 42. so that when the pressure in the pipe 5| which is at all times in communication with the upper ends of the auxiliary cylinders 2|. becomes sui'licient to overcome the pressure of the spring 55 on the valve element 54, the valve element 54 will open and liquid will pass through pipes 59 and 42 back to the tank 32. As soon as the excess pressure falls the spring 55 will again close the valve element 54, and hence the pressure in the upper ends of the cylinders 2| and thus on the blank holding ring l1 will be sustained, and will be directly proportional to the pressure of the spring 55 on the valve element 54. Thus the pressure on the ring |1 may be varied by rotating the stem or rod 51 in one direction or the other, depending upon whether an increase or decrease in the pressure of the ring H on the blank I 6 is desired.

In order to vary the pressure on the Spring 55 and thus the pressure of the ring H on the blank l6, the outwardly extending end of the rod or stem 51 is provided with a pinion 60 which meshes with the teeth of a rack bar 6 I The bar 6| is rockably connected at its lower end to one arm of the bell crank lever 62, pivoted at 63, and mounts upon its other arm a cam follower or roller 64. A spring urges the bell crank lever 62 yieldingly in a direction to force the cam follower 64 against a cam surface 66 which moves in timed speed ratio to platen l2 and in the simple embodiment shown is carried by the platen l2.

As the platen I2 moves toward the die element It, the undulations of the cam surface 66 which moves concurrently with the platen either at the same speed or in some multiple or submultiple thereof cause a rocking of the bell crank lever 62, reciprocation of the rack bar 6|, and rotation of the pinion 60 and of the stem or rod 51, to change the pressure on the blank holding ring IT in accordance with .a predetermined plan under the control of the platen l2. Thus while the ring l1 remains clamped against the blank I 6 under a sustained hydraulic pressure, the travel of the platen in a downward direction will cause a variation in this sustained pressure in accordance with a predetermined plan.

The connection between the rack bar 6| and the bell crank lever 62 is one which causes the rack bar to reciprocate vertically in both directions upon rocking of the bell crank lever 62. For example, the rack bar may have a shoulder or collar 61 provided thereon at a short distance from the lower end of the bar and engaging with one side of the bell crank arm, and the bar, after passing loosely through an aperture or slot in V the arm of the bell crank lever 62, carries a washer 68 and a nut 69. Thec01lar 61 and the washer 68 have semi-spherical or convex arcuate surfaces abutting opposite faces of the bell crank lever 62, so that the rack bar may rock laterally somewhat at its connection to the bell crank 62.

The valve 23 is similar inconstruction to the valve 22, and is provided with a central annular port 1|) and intermediate ports 1| and 12. The valve element 13 is of spool shape, similar to the valve element 25 of valve 22, and has the flange 14 at one end, which corresponds to the flange 41 of valve 22, of such thickness that when in its neutral position shown in Fig. 1,'it will bridge and close the port 1|. The other flange 15, which corresponds to the flange 38 of valve 22, is bevelled or chamfered on both faces at its periphery for a similar purpose, so that when the valve element 13 is in a neutral or. intermediate position, such as shown in Fig. 1, in which the flange 14 closes the port 1|, the chamfered flange 15 will be aligned with the port 12. Liquid may thus pass from the port 10 around the flange 15 at the port 12, through the upper end of the valve chamber 16, and thence through the pipe 40 to the tank 32.

A unidirectional, continuously operating pump 11 is connected at its intake side by a pipe 18 to a portion of the tank 32 at a point spaced from the connection of the pipe 40 to the tank. The output or delivery side of the pump 11 is connected by a pipe 19 to the port 10, so that when the valve element 13 is in the neutral position shown in Fig. 1, the liquid delivered by the pump 19 will flow around the periphery of flange 15 and back through the pipe 40 to the tank, thus circulating idly through the valve chamber 16. The port 1| is connected by a pipe to the lower end of the main cylinder M, and thus liquid trapped in the cylinder I4, below the head thereof, cannot escape through the port 1| which holds the platen l2 in raised position.

Pipe 40 is also connected by a branchpipe 8| to the lower end of the chamber 16, for a purpose which will appear presently. The valve element 13 is reciprocated endwise in the chamber 16 by means of a valve rod 82 which extends downwardly through the lower end of the chamber 16, passes through an aperture 83 in the platen l2, and at its lower end is pivotally connected by a pin 84 to one end of a control lever 85, which in turn is pivoted at 86 to a suitable support.

When a downward movement of the platen is desired the operator pushes the free end of the control lever 85 downwardly. which elevates the rod 82 and through it shifts the valve element 13' from the neutral intermediate position shown in Fig. 1 to the upper position shown in Fig. 8. When this occurs the flange 14 uncovers the port II and positively prevents communication between the ports 10 and 1|. however, established between the pipes 86 and 8| Communication is,

so that the fluid trapped in the lower end of the main ram cylinder I4 may escape through the pipe 89, the port II, the chamber 16, and pipes 8| and 49 back to the tank 32.

At the same time the flange 15 moves above the port 12 and the liquid deliveredby the pump 11 instead of passing upwardly and around the flange 15 to the pipe 49 will be compelled to pass through the port 12, and thence by means of pipes 81 and 99 to the upper end of the main cylinder I4. The movement of operating fluid into the upper end of the cylinder I4 and the weight of the platen I2 will cause the platen to descend as rapidly as fluid can enter the upper end of the cylinder I4.

In order that the speed of the platen I2 may be rapid until the drawing operation starts, the

pipe 38 is connected through a prefill check valve 99 to the pipe 49 and thus to the tank 32. This valve 89 is identical with, except usually larger than, the valve 41 shown in Fig. 3 and it opens freely in a direction to pass fluid from the pipe 49 to the pipe 38 and the main cylinder I4, so that as the descent of the platen creates a suction in the upper end of the cylinder I4, operating liquid may flow from the tank 32 through the pipe 49, the valve 89 and pipe 98 into the upper end of the cylinder I4, thus supplementing the liquid delivered by the pump 11 to the upper end of the cylinder I4.

When the die I5 carried by the platen I2 engages with the blank I6, pressure resistance to further movement of the platen I2 is set up, and since the pump 11 continues to deliver liquid to the upper end of the cylinder I4, the pressure on the upper end of the piston I3 will build up, whereupon the liquid in the cylinder I4 will tend to flow outwardly through the pipe 88 and valve 89 to the pipe 49, but thereupon the valve 89 closes automatically, so that the pressure on the upper end of the piston I3 builds up in response to the continued delivery of liquid to the upper end of the cylinder I4 from the pump 11.

It is desirable to vary the speed of downward travel of the platen during the drawing operation on the blank l6, and the means for varying this speed in accordance with a predetermined plan will next be described. The pipe 99 connects the pipe 81, leading from the port 12, to one end of a by-pass valve 9I which is shown diagrammatically in Fig. 1 and in greater detail in Fig. 4. In the chamber 92 of the valve 9I is a valve element 93 which is mounted on the end of a stem or rod 94. The rod 94 has threaded engagement with the inner end of a sleeve 95 that closes one end of the chamber 92. Thus as the stem 94 is rotated, it will be threaded into and out of the chamber 92 to various extents, so as to shift the valve element 93 toward or from its valve seat in the chamber 92, depending upon the direction of rotation of the stem 94.

A pipe 96 connects the chamber 92 to the pipe 49, from which it will be observed that a portion of the liquid delivered by the pump 11 to the pipe 91 may pass through the pipe 99 and the pinion 91 which meshes with the teeth of a rack bar 99. This rack bar depends from the pinion 91 and at its lower end is rockably connected to one arm of a bell crank lever 99, such-as in the manner explained for the connection of the rack bar 6| to the bell crank lever 62'.

The bell crank lever 99 is pivoted at I99, and its other arm carries an offset cam roller or 01- lower I9I which engages with and rolls upon a cam surface I92 that moves concurrently with the platen in timed speed ratio thereto, that is, at the same speed or a speed which is a multiple or submultiple of the platen speed. If the same speed is desired, the cam surface I92 may be carried by the platen I2. A spring I93 that is connected to the horizontal arm of the bell crank 99, urges the latter in a direction to press the roller I9I against the undulating cam surface I92 at all times. The cam surface I92 extends or undulates in the direction of the travel of the platen, and thus as the platen I2 descends, the cam surface I92 thereof will cause'a rocking of the bell crank 99 and through the resulting reciprocation of the rack bar 98, the pinion 91 and stem 94 will be turned in one direction or the other to increase or decrease the amount of liquid by-passed. When more liquid is by-passed, the speed of travel of the platen I2 will be decreased, and vice versa.

Thus the platen I2 in its movement controls its own speed during the drawing stroke, and by selecting the undulations of the cam surface I92, the speed of travel of the platen I2 may be decreased at those points or zones in the drawing operation, where there is danger of tearing or rupturing of the blank, with the result that deeper draws may be successfully made. By selecting the character of the cam surface 66, the pressure of the blank holding ring I1 on the periphery of the blank I6 may be decreased to the extent desired in the proper zone of the platen travel to allow more slippage of the blank I6 at the critical zones, which in some cases may be at the same time that the speed of the platen I2 is decreased. Any other control of the pressure of the blank holding ring on the blank or in the speed of the platen may be obtained merely by proper selection of the shapes of the cams 66 and I 92. Since the critical zone is reached at an intermediate point in the drawing operation, the pressure on the blank will usually be set to hold the blank under a selected pressure until this critical but intermediate point or zone in the-drawing operation is reached and then the pressure on the entire blank is partially, but not fully, released, to allow just the amount of slippage desired that will prevent tearing or rupture of the blank.

At the end of a drawing operation the operator elevates the upper end of the control lever 85, which pulls the valve rod 82 downwardly and moves the valve element 13 from the position shown in Fig. 8 to the position shown in Fig. 9. When this occurs the flange 15 will cut off communication between the ports 19 and 12, thus interrupting delivery from the pump 11 to the upper end of the main cylinder I4, and the flange 14 will move concomitantly to a position between the port H and the outlet pipe 8|, so that escape of further liquid from the lower end of the cylinder I4 will be prevented. The central port 19 is now connected to the port 1|, and thus the liquid delivered by the pump 11 to the valve chamber 16 will now pass through the port 1| to the pipe 89, and thence to the lower end of the ducting the liquid delivered cylinder l4, so as to exert a lifting pressure on the piston l3. The flange I has moved from a position in which it interrupted communication between the port I2 and the pipe 40, so that the liquid previously delivered to the upper end of the cylinder l4 may now pass through the pipes 88 and 81, the port 'I2 and the pipe 40 back to the tank 32. The pressure in the upper end of the cylinder l4 thus immediately falls and permits an upward movement of the piston l3.

In order to expedite the upward movement of the platen l2, pr'ovisionis made for forcibly opening the check valve of .the prefill valve 89. For

this purpose a branch pipe I04 leads from the pipe 80 to the pilot cylinder of the prefill valve 89 so as to forcibly open the check valve element 58 thereof in the manner hereinbefore explainedfrom the die recess 1y from the upper ends of the auxiliary cylinders 2| to the pipe 40 and back to the tank. After the blank holding line H has been elevated, the formed blank l8 may then be-eiected in any suitable manner which is common in the art, such as by a spring ejector or air or hydraulic mechanism, not shown, and which in itself forms no part of this invention.

As the l1 approaches its upper-limit of movement it engages the collar 38, shifts the valve stem or rod 26 upwardly, and thus returns the valve element 25 from the Fig. 7 position to the Fig. 1 position which isthe idle or neutral position occupied when the press is idle. At this time the pump 33 circulates liquid idly through .the valve 22 and pipes 38 and 40 back to the in connection with the'opening of the prefill valve 41.

As the platen |2 moves upwardly and approaches its upper limit of movement, it will engage with a collar I85 provided on the valve rod positions by 82, so that further upward movement of the platen l2 will elevate the rod 82 and shift the valve element 13 from the position shown in Fig. 9 to the neutral or idle position shown in- Fig. 1. When the valve element T3 moves back into this neutral position, the flange 14 again bridges the port II and thus disconnects the pump 11 from the pipe 8|], and also prevents escape of liquid from the pipe 80, thus locking the main piston l3 in its elevated position. The flange 15 at the same time opens communication from the port 10 to the port .12 and the pipe 40, thus conback to the tank 32. This idle circulation of liquid-through the pump 11 will continue and the piston l3 will be effectively held in its eievated position. The collar I05 is mounted on the rod 82 for adjustment endwise along it, and it may be secured in different adjusted positions in any suitable manner such as by a set screw which is carried by the collar and is engageable with the rod 82.

When the platen l2 starts upwardly the blank holding ring I! will continue to hold the blank l6 against the die element I0, so as to strip the formed blank from the die element l5, and after that occurs the operator elevates the free end of the control lever 28 which shifts the valve element 25 from the position shown in Fig. 6 to the position shown in Fig. 7. When this occurs,

the intermediate port 36 to which the pump 33 delivers operating liquid will'be connected with the port 43, and thus the liquid from the pump will be delivered through the pipe 44 to the lower ends of the auxiliary cylinders 2|. At this time the flange 38 is disposed between the ports 36 and 46 and shuts off communication between them, but places the port 45 in communication with the pipes 39 and 40.

The liquid in the upper ends of the auxiliary cylinders 2| may then pass through the pipe 45, through the port 46, and pipes 39 and 40 back to the tank 32, and thus as the liquid is delivered under pressure to the lower ends of the auxiliary cylinders 2|, the auxiliary pistons I9 will be elevated and thus will elevate the blank holding ring or element l1 and release the blank Hi.

The pressure of the liquid from the pump 33 is transmitted through the pipe 44 to the pilot cylinder 41a, and will force the pilot piston 41b upwardly against the action of the spring 410. This forcibly opens or lifts the check valve element 58, so as to allow the liquid to pass directby'the pump 11 1 tank 32, and the pistons I8 are held in their upper the liquid trapped in the lower portions of the auxiliary cylinders 2|, due to the bridging of the port 43 by the flange 31 of the valve element 25. The operation of the press and system will be clear from the foregoing description, but may be briefly summarized as follows:

Assuming thatvth'e parts are in the idle position shown in Fig. 1, let it be assumed that a blank l6 has been placed on the die element l-ll across the die recess The operator then depresses the free end of the control lever 28, which elevates the valve element 25 and initiates a downward movement of the auxiliary pistons l9 and ring At the start of this downward movement of ring H, the pressure on the pipe 44 is released, and thus the pressure on the pilot piston 41b is decreased, whereupon the spring 410 forces the pilot piston 41b downwardly to release the check valve element 50, and permit it to close. When the ring l1 engages with the blank Hi, the pressure then built up in the upper ends of cylinders 2| causes the prefill valve 41 to close, and the continued delivery of, liquid from the pump 33 to the upper ends of the auxiliary cylinders 2| will build up a sustained pressure upon th blank holding ring I1, until the pressure is suflicient to overcome the force of spring 55, whereupon the valve element 54 opens sufficiently to maintain the pressure at that determined by the setting of the pressure head 56.

When the blank holding ring has progressed far enough so that it will engage and hold the blank l6 before the platen l2 can carry the die element l5 into engagement with the blank, the operator depresses the free end of the control lever 85, which elevates the valve element 73 from the Fig. 1 position to the Fig. 8 position, and initiates a downward movement of platen l2. The downward movement of the platen |2 will be controlled at intervals in. its descent as to speed by the cam surface I02 and the bypass valve 9|, the latter being set into different degrees of opening by successive changes in the character of the surface I82 as the platen I2 descends. At the same time the pressure on the blank holding ring will vary in accordance with the successive positions of the platen 2 under the control of the cam surface 66.

At the end of the drawing operation, the operator elevates the free end of the control lever 85 and initiates an upward travel of the platen l2 that is terminated automatically by engagement of the platen with the collar I05, through which the rod 82 is elevatedto return the valve r element 13 to the neutral position shown in Fig. 1. The upward movement of the blank holding ring is initiated after the platen I2 has started upwardly, by tilting upwardly the free end of the control lever 28, and the upward movement of the ring I1 'is terminated when it .engages the collar 30 and elevates the rod 26 sufllciently to return the valve element 25 to the neutral position shown in Fig. 1.

The shape and configuration of the cam surfaces 66 and I02 will vary with different dies employed. because the slippage and speed of travel must be varied at just the critical points in the drawing operation. These critical points will vary with different types of blanks being drawn and difierent dies that are used, and must be determined for each different die or blank employed.

In Fig. 10 a slight modification of the controls of the pressure on the blank and of the travel of the platen have been illustrated with so much of the remainder of the press and system as is necessary to show the relation of the modified parts to the other parts. In this modification of Fig. 10, the pressure opened valve 53 and the pipes 5| and 59 shown in Fig. 1 are omitted, and the pump 33 is replaced by a pump I05 which is of the variable delivery reversible type, but continuously operating. Such pumps are well known in the art and by way of example, One of this general type is illustrated in U. S. patent to Landenberger et a1 #1,863,448 issued June 14, 1932. The pump at its intake side is connected by the pipe 34 to the tank or source 32 of operating liquid, and its output side is connected by the pipe 35 to the valve 22, as in Fig. 1.

The pump I05 is adjustable in order to vary its delivery or to reverse its delivery by means of a yoke I06 which is shifted in alternate directions by a lever I01 pivoted at I08. The lever I01 is pivoted to a block I09 which is mounted on a rod I I to slide in a direction endwise thereon. A nut or collar III is provided on an end of the rod IIO so as to limit movement of the rod H0 with the block I09 in one direction, and a helical spring H2, disposed on the rod H0 and acting against a washer or collar H3 that is slidably mounted on the rod H0, forces the block I09 yieldingly against the nut or collar III. Pressure is provided on the spring H2 by a washer H4 which is slidable on the rod H0 and abuts endwise against a pinion H5 that is threaded on the rod H0. Thus, by rotating the pinion H5, it will be threaded along the rod H0 so as to further compress or release the spring H2, and thus vary the pressure with which the lever I01 is held against the collar or nut III.

A lever H5, pivotally mounted at H1, is pivoted at one end by a pin H8 to a block H0 that is also threaded or fixed on the rod H0, so that the rod H0 may be forcibly operated in alternate directions to change the direction of delivery of the pump, or the rate of delivery, in a manner which is well known in the variable delivery reversible type of pumps. The pressure in the pipe 35, which is the output side of the pump as connected, is operable upon the lever I01 through a small ram, not shown, but which is common in this type of pump, in a manner to rock the lever I01 clockwise in Fig. 10, against the action of the spring H2, while the rod |lI0 remains in set position. Thus, when the pressure in pipe 35 equals or exceeds a predetermined pressure, determined by the pressure of spring H2, the lever I01 will be rocked clockwise in Fig. 10 against the action of spring H2 so as to shift the yoke I06 in a direction to set the pump for neutral delivery position.

If the pressure falls, the spring II! will return the lever I01 and yoke I00 to delivery position, and the pressure in pipe 35 will be built up until it is again sufficient to overcome the pressure on spring II2.- By rotating'the pinion H5, one may therefore determine the pressure which will be maintained automatically in the pipe 05, and this pressure may be varied merely by rotating the pinion H5 in one direction or the other, depending upon whether an increase or decrease of pressure is desired. The pinion H5 meshes with the rack bar BI corresponding to the rack bar SI of Fig. 1, and thus, as the platen I2 moves downwardly the cam surface 56 will operate the rack bar 6| to change the pressure on the spring I I2 in accordance with a predetermined plan and controlled by the travel of the platen, thereby determining the pressure on the blank during the drawing operation, which pressure varies with the different positions of the platen in accordance with a predetermined plan. The lever H6 is operated merely to change the maximum rate of delivery of the pump, and the reversing feature of the pump need not be utilized.

In controlling the rate of travel of the platen in the working stroke under the system as modified in Fig. 10, the valve 9| and pipes and 96 of Fig. 1 may be omitted, and the pump 11 of Fig. 1 is replaced by a pump I20 of the variable delivery reversible type in Fig. 10. The reversible feature need not be utilized in the system. The intake side of the pump is connected to the pipe 18, as in Fig. 1, and the output side of pump is connected by the pipe 19 to the valve 23, also as in Fig. 1. The pump I29 is identical with the pump I05 except that instead of the pinion H5 in the control for the pump I05, I have substituted a hand wheel I2I which is threaded on the rod H0 for varying the pressure on the spring I I2. The rod I I0 which varies the rate of delivery of the pump is connected to a lever I22 which corresponds to the lever H6 of the pump I05 except that the lever I22 is a bell crank lever and is pivotally connected by a pin I23 to one end of a link I24 which corresponds to the rack bar 98 of Fig. 1. Thus, as the platen I2 moves downwardly, the cam surface I02 thereof will act through the roller IOI and link I24 to shift the rod H0 endwise and thus change the rate of delivery of the pump which controls the speed of travel of the platen. Otherwise the system is the same as in Fi 1.

It will be understood that the various changes in the details, materials and arrangements of parts, which have been herein described and illustrated in order to explain the nature of the invention, may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims.

I claim as my invention:

1. The method of drawing a metal blank into a desired shape and size by the relative movement of two dies, which comprises clamping said blank against one of said dies, drawing said blank to the desired size and shape by relative movement between said dies, and varying the rate of relative movement of said dies in their action on the blank and releasing the clamping pressure of said blank against said one die sufliciently to allow limited and controlled slippage of the blank on said one die in correlated relation to one another, whereby unusually deep draws may be made in the blank without tearing of the blank..

2. The method of drawing a metal blank into a desired shape and size by the relative movement of the two dies, which comprises clamping said blank against one of said dies, drawing said blank to a desired size and shape by relative approach 01 said dies toward one another with the blank between them, decreasing the rate of approach between said dies after the blank has been partially drawn and before the drawing has been completed, releasing the clampin pressure on said blank by said one die sufficiently for the blank to slip on that die to a limited and controlled extent, while the dies occupy particular predetermined positions in the zone where the rate of relative approach of the dies has been decreased, and controlling the decrease in the rate of approach of the dies and of the release of the clamping pressure in correlated relation to the relative movement of the dies, whereby relatively deep draws of metal may be made without tearing of the blanks.

3. The method of drawing a metal blank into a desired shape and size by the relative movement of the dies, which comprises clamping said blank against one of the dies, drawing said blank to a desired size and shape by the relative approach of said dies toward one another with the blank between them, and partially, but not fully, releasing the clamping pressure and slowing down the rate of approach of said dies at a critical zone of the drawing operation sufficiently to prevent tearing or rupturing of the blank and enable deeper draws successfully.

4. The method of drawing a metal blank into a desired'shape and size by the relative movement of the dies, which comprises clamping said blank against one of the dies, drawing said blank to a desired size and shape by the relative approach of said dies toward one another with the blank between them, and decreasing the rate of approach of the dies and concomitantly releasing the blank sufliciently for regulated slippage of the blank in critical zones of the drawing operation.

5. The method of drawing a metal blank into a desired shape and size by the relative movement of the dies, which comprises clamping said blank against one of the dies, drawing said blank to a desired size and shape by the relative approach of said dies toward one another with the blank between them, and decreasing the rate of approach of the dies and releasing the blank sufficiently for regulated slippage of the blank solely in critical zones of the drawing operation.

6. The method of drawing a' blank between opposing dies to make a stamping having considerable depth in the direction of travel of the moving die, which comprises clamping said blank against one die under a sustained holding pressure, drawing said blank to a desired size and shape by the relative approach of said dies towards one another, providing regulated slippage of said blank by partial release of said holding pressure at a critical, intermediate point in the drawing operation after the blank has been partially shaped, when regulated slippage of the blank is desirable to avoid rupture or tear of the blank being drawn, and reducing the speed of approach of said dies at an intermediate point during the drawing operation when the stresses in said blank may closely approach those at which the blank being drawn may tear or be ruptured.

THOMAS F. STACY. 

